PROJECT/SUMMARY ABSTRACT A major issue in the management of brain tumors is their aggressive growth and invasion into surrounding normal brain tissue. Unfortunately, our understanding of the mechanisms that underlie the aggressive behavior of these tumors is very limited. Recent evidence indicates that the invasiveness of solid tumors involves signaling events downstream of Rho GTPases. The Rho family of small GTPases in general and RhoA in particular, are critical regulators of directed cell migration, cell division, and monolayer patency. Our basic research findings on the mechanics of cell migration have identified the Rho guanine exchange factor (GEF) Syx as important in promoting directed cell migration, via its interaction with members of the Crumbs polarity complex, and activation of RhoA signaling. Interestingly, Syx is highly expressed in human gliomas. Preliminary studies show that in addition to suppressing cell migration, depletion of Syx drastically impairs glioma cell division, and significantly improves animal survival in a xenograft mouse model of GBM. Additionally, inhibition of Syx signaling in cultured glioma cells strongly synergizes with Temozolomide (TMZ), the standard of care therapy for GBM. The overall scientific premise of this project is that Syx signaling plays a key role in GBM cell growth, migration and invasion, as well as in responsiveness to chemotherapeutics. As such, we hypothesize that therapeutic targeting of the Syx-RhoA signaling axis can suppress both the aggressive growth and invasion of human gliomas and synergize with standard-of-care therapy. To further characterize the role of Syx in the aggressive growth and invasiveness of human GBM and to test the efficacy of targeting Syx signaling in combination with standard GBM therapy, we will use cultured cells, organotypic cultures, animal models of human GBM, as well as human GBM tissue samples, to: 1. Characterize the effect of Syx depletion on GBM aggressiveness. 2. Identify key additional components of the Syx-RhoA signaling axis. 3. Determine whether inhibition of Syx can enhance the efficacy of chemotherapeutics.